New structure of L-cysteine self-assembled monolayer on Au(111): Studies by in situ scanning tunneling microscopy

A self-assembled monolayer of L-cysteine was prepared on Au(111) under pote ntial control. Cyclic voltammetry and in situ electrochemical scanning tunn eling microscopy were employed to investigate the molecular adsorption and adlayer structure in perchloric acid solution. The molecules chemically ads orb on Au(111) and form a well-defined adlayer. A new structure of (4 x roo t7)R19 degrees was observed in the double-layer region. A phase transition at the positive potential region resulted in the appearance of a disordered layer. A structural model is proposed to interpret the molecular registry with Au(111) substrate.